The present invention is directed to a machine tool having a compartment containing lubricant and a device for compensation of the pressure in the compartment.
A machine tool forming the species, in particular a hand-operated hammer drill, is known from German Published Patent Application No. 42 31 987. The hammer drill has a driver motor, arranged within a motor compartment of a housing, having a motor shaft that extends through a housing section into a gear compartment, where it engages, via an integral pinion, with a gear unit for driving a tool-holding fixture. The gear compartment is provided with a pressure-compensation device that reduces a pressure, resulting during operation within the gear compartment, down to that of the atmosphere or of the motor compartment. The pressure-compensation device has a bore hole leading from the gear compartment to the outside or to the motor compartment and a rotary element, driven so that it is constantly rotating, in the form of a cover into which a passage is introduced.
The present invention is directed to a machine tool, in particular to a hand-operated hammer drill, having a compartment containing lubricant and a pressure-compensation device of the compartment in the area of a bearing of a component able to be driven so as to allow rotation.
It is proposed that the bearing form at least a part of a lubricant seal of the pressure-compensation device via which a pressure in the compartment may be compensated. Additional components, space, weight, assembly effort and costs can be saved. This can be achieved in a particularly inexpensive and uncomplicated manner in terms of design by using a lubricant seal implemented as a groove seal, which is arranged between the bearing and a bearing seat, it being possible to arrange the groove seal between an outer ring and/or an inner ring of the bearing and a bearing seat. Furthermore, it is conceivable that the lubricant seal, which is simultaneously usable for pressure compensation, is formed by a channel through the bearing, for example, a channel through a cage of a roller bearing and/or through bearing sealing washers fastened appropriately to the bearing.
In another embodiment of the present invention, it is proposed that the bearing and the bearing seat be formed of different materials having different coefficients of thermal expansion and that these be used to create the lubricant seal; specifically, it is beneficial that the bearing seat is formed of aluminum or an aluminum alloy and the bearing is formed of steel. If an outer bearing seat is formed of a material having a greater coefficient of thermal expansion than the bearing, as is beneficially the case for an aluminum bearing seat and a steel bearing, the bearing seat expands more when heated up and a gap between the bearing and bearing seat is created that may beneficially be used as a groove seal. Other material combinations that appear suitable to one skilled in the art are also conceivable in place of an aluminum-steel combination.
In this context, to prevent an undesired rotary movement of the bearing within the bearing seat, it is beneficially fixed in position in the circumferential direction within the bearing seat. This may be accomplished using various non-positive fit, positive fit and/or integral connections, for example, via a pin connection, a spring/groove connection and/or a positive-fit connection, in that an outer ring of the bearing has an outer contour that deviates from a round outer contour, etc. If the bearing is implemented as a locating bearing, and a component fixing the bearing in position in an axial direction is used to fix the bearing in position in the circumferential direction, additional components, space and assembly effort may advantageously be saved. For example, this can be achieved using a clasping component that holds the bearing in position in an axial direction, is torsionally fixed and has a projection that engages in a recess of an outer ring of the bearing.
In another embodiment of the present invention, it is proposed that a pressure-compensation channel be introduced into a bearing surface of the bearing and/or into a bearing surface of the bearing seat. A beneficial cross-section for the pressure compensation may be achieved with simplicity of design, and simultaneously a groove seal and/or labyrinth seal may be realized. The pressure-compensation channel in this case may be implemented, for example, in the form of an axial groove in a shaft, in an inner ring of a roller bearing, in an outer ring of a roller bearing and/or in a component forming an outer bearing seat, etc.
If the pressure-compensation channel is at least partially formed by a threaded-type recess, a beneficial labyrinth effect or labyrinth seal and, in addition, a recirculating effect may be achieved, which is done by coordinating the direction of threading and direction of rotation with each other. The threaded-type recess may in turn be introduced into the bearing and/or into a bearing seat. If the pressure-compensation channel opens through into at least one annular groove, it may be produced especially simply and economically, for example in one lathe operation, starting from a first annular groove and opening through into a second annular groove.
A filter element is beneficially connected in series with the lubricant seal formed at least partially by the bearing. While simultaneously ensuring the pressure compensation function, the sealing effect can be improved. A felt gasket, which can be manufactured especially economically and has proven beneficial characteristics, is especially suitable as a filter element. The felt element may be formed by various fibrous materials deemed appropriate by one skilled in the art, in particular such as animal hairs, plant fibers and/or synthetic fibers, etc. In order to save on additional holding components, the filter element is beneficially held in position by a component that holds a bearing in place.
Furthermore, in a space-conserving design, a beneficially large filter volume can be achieved, in that at least two radial pressure-compensation channels branch off from the bearing, and in particular in that the bearing is surrounded by an annular filter element, and the pressure-compensation channels open out from the bearing radially outwardly at the filter element.
The design approach of the present invention may be used in all machine tools deemed suitable by one skilled in the art, in particular in hand-operated machine tools, for example, grinders, saws, milling cutters, planers, drills, chisel hammers, etc.